U.S. patent number 6,042,956 [Application Number 08/880,414] was granted by the patent office on 2000-03-28 for method for the simultaneous generation of electrical energy and heat for heating purposes.
This patent grant is currently assigned to Sulzer Innotec AG. Invention is credited to Daniel Lenel.
United States Patent |
6,042,956 |
Lenel |
March 28, 2000 |
Method for the simultaneous generation of electrical energy and
heat for heating purposes
Abstract
A method for the simultaneous generation of electrical energy
and heat for heating purposes uses a combustion gas consisting
mainly of one or more hydrocarbons as well as a gas mixture
containing oxygen. The method is carried out by means of at least
one gas burner and at least one stack of fuel cells, with an oxygen
surplus having a stoichiometric ratio greater than about 3 being
provided in the battery. In the battery less than half of the
combustion gas is converted for the generation of electricity while
producing a first exhaust gas. The remainder of the combustion gas
is burned in the burner while producing a second exhaust gas, and
the first exhaust gas is used at least partially as an oxygen
source for the combustion. Heat energy is won from the exhaust
gases, with at least about half of the water contained in the
exhaust gases being condensed out.
Inventors: |
Lenel; Daniel (Baretswil,
CH) |
Assignee: |
Sulzer Innotec AG (Winterthur,
CH)
|
Family
ID: |
8225646 |
Appl.
No.: |
08/880,414 |
Filed: |
June 23, 1997 |
Foreign Application Priority Data
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Jul 11, 1996 [EP] |
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96810448 |
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Current U.S.
Class: |
429/425; 429/429;
429/440; 429/441; 429/444; 429/452; 429/901 |
Current CPC
Class: |
F24H
1/0027 (20130101); H01M 8/04007 (20130101); H01M
8/0625 (20130101); H01M 8/04014 (20130101); Y02E
60/50 (20130101); Y10S 429/901 (20130101); F24H
2240/10 (20130101); H01M 8/04022 (20130101) |
Current International
Class: |
F24H
1/00 (20060101); H01M 8/04 (20060101); H01M
8/06 (20060101); H01M 008/04 (); H01M 008/22 () |
Field of
Search: |
;429/19,26,23,24,17 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 486 911 A1 |
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May 1992 |
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EP |
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0 654 838 A1 |
|
May 1995 |
|
EP |
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44 46 841 A1 |
|
Jul 1996 |
|
DE |
|
WO 94/18712 |
|
Aug 1994 |
|
WO |
|
9418712 |
|
Aug 1994 |
|
WO |
|
Other References
Winkler, W. "Kraftwerke mit Brennstoffzellen als neuer
Kraftwerkskomponente", in: VGB Kraftswerktechnik, vol.
75(6):509-515 (1995) Month N/A. .
Extended Abstracts, vol. 87-02, Oct. 18, 1987, pp. 261-262,
Krumpelt M., et al. "Systems Analysis for High-Temperature Fuel
Cells". .
General Chemistry, by Darrell Ebbing ,Houghton Mifflin Company, p.
216, 1996..
|
Primary Examiner: Nuzzolillo; Maria
Assistant Examiner: O'Malley; J.
Attorney, Agent or Firm: Townsend and Townsend and Crew
LLP
Claims
What is claimed is:
1. A method for the simultaneous generation of electrical energy
and heat for heating purposes from a combustion gas comprised of
one or more hydrocarbons as well as a gas mixture containing
oxygen, by means of at least one gas burner and at least one stack
of fuel cells, with an oxygen surplus having a stoichiometric ratio
greater than approximately 3 with respect to the hydrocarbons being
provided in the stack of fuel cells the method comprising,
converting less than half of the combustion gas in the stack for
the generation of electricity while producing a first exhaust gas;
burning the remaining part of the combustion gas in the burner
while producing a second exhaust gas; using the first exhaust gas
at least partially as an oxygen source for the combustion; and
gaining heat energy from the exhaust gases, with at least
approximately half of the water contained in the exhaust gases
being condensed out; wherein the two exhaust gases are mixed
directly upon their leaving the stack of fuel cells and the burner
respectively, the exhaust gas mixture being conducted into a heat
exchanger in which heat for heating purposes is removed from the
mixture while water vapor is condensed; and
wherein subsequently a portion of the cooled mixture is conducted
back to the burner for the combustion.
2. A method in accordance with claim 1 wherein the combustion gas
comprises methane; wherein the gas mixture containing the oxygen is
air; and wherein at least approximately 6 moles of molecular oxygen
as well as 1 mole of water are fed in to the stack of fuel cells
per mole of methane.
3. A method in accordance with claim 2 wherein at least 2.2 moles
of molecular oxygen per mole of methane are fed in to the
burner.
4. A method in accordance with claim 1 wherein at least a portion
of the first exhaust gas is supplied to the burner without prior
removal of heat.
5. A method in accordance with claim 1 wherein the first exhaust
gas from the stack of fuel cells is conducted into a heat exchanger
in which heat for heating purposes is removed from the exhaust
gas.
6. A method in accordance with claim 1 wherein combustion gas of
the burner is used for the heating of the fuel cells to operating
temperature during a start up phase.
7. A plant comprising a stack of fuel cells, a burner, at least one
heat exchanger for exhaust gases which arise in at least one of the
burner, the stack of fuel cells, and at least one consumer system
for the utilization of the heat gained from the exhaust gases, with
a connection being provided from the stack of fuel cells to the
burner for the exhaust gas, wherein less than half of combustion
gas supplied to the stack of fuel cells is converted in the stack
of fuel cells and the remaining portion of the combustion gas is
burned in the burner; wherein the plant is configured such that the
exhaust gases are mixed directly upon their leaving the stack of
fuel cells and the burner respectively, the exhaust gas mixture
being conducted into a heat exchanger in which heat for heating
purposes is removed from the mixture while water vapor is
condensed; and wherein the plant is configured such that
subsequently a portion of the cooled mixture is conducted back to
the burner for the combustion.
8. A plant in accordance with claim 7 wherein the consumer system
comprises a utility water heater and a room heating system.
9. A plant in accordance with claim 8 wherein the utility water
heater stands in active contact with an exhaust gas line of the
stack of fuel cells.
10. A plant in accordance with claim 7 wherein a lambda probe is
provided at the output of the burner for determining the oxygen
content of the exhaust gas; and wherein the probe is a component of
a control system by means of which supply of the combustion gas
and/or of the exhaust gas from the fuel cells into the burner is
regulated.
11. A plant in accordance with claim 7 wherein the stack of fuel
cells contains a channelling system for heating up the stack of
fuel cells during a start up phase; and wherein the channelling
system can be connected to the exhaust gas line of the burner.
12. A plant in accordance with claim 7 wherein the stack of fuel
cells comprises a centrally symmetrical cell stack as well as a
prereformer placed ahead of the stack for the combustion gas.
13. A plant in accordance with claim 7 wherein the connection for
the exhaust gas is a direct connection.
14. A plant in accordance with claim 7 wherein the connection for
the exhaust gas is an indirect connection.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for the simultaneous generation
of electrical energy and heat for heating purposes from a
combustion gas, part of which is converted in a battery while the
other part is burned in a burner as well as to a plant for carrying
out the method.
2. Summary of the Prior Art
When using natural gas for heating purposes, in particular for
heating rooms and/or utility water, the gas, which contains at
least about 80% methane, is generally burned. Advantage is not
taken here of the possibility of generating high quality energy, in
particular electrical energy. It is however known that up to 50% of
the chemical energy of methane can be converted to electrical
energy by means of fuel cells. In high temperature cells the
simultaneously arising heat to be dissipated can be economically
used for heating purposes. Instead of natural gas, a combustion gas
containing a hydrocarbon can also be used in which at least a
portion of the gas consists of a hydrocarbon other than
methane.
In many instances a supply of electrical energy which is largely
constant throughout the entire year is desirable. If one intends
simultaneously to generate electrical energy and heat for heating
purposes by means of fuel cells, one is confronted in regions where
heat is required for heating rooms only in the winter, i.e. in the
cold season when substantial amounts of heat are required for
heating the rooms, with the problem that large amounts of
electrical energy can be generated during the winter, for the
economical use of which it is difficult to find consumers. It is
thus advantageous to combine the use of fuel cells with the use of
conventional heating devices, in particular gas burners. During the
warm season then the fuel cells can be operated alone; the heat
given off can be used for heating the utility water.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method for a
combination of this kind, which comprises the use of fuel cells and
gas burners, which makes available a large amount of heat for
heating purposes especially during the winter, where the
simultaneous generation of electricity by the fuel cells is to be
carried out at the maximum possible power level.
The method for the simultaneous generation of electrical energy and
heat for heating purposes uses a combustion gas consisting mainly
of one or more hydrocarbons as well as a gas mixture containing
oxygen. The method is carried out by means of at least one gas
burner and at least one stack of fuel cells, with an oxygen surplus
being provided in the battery at a stoichiometric ratio greater
than about 3. Less than half of the combustion gas is converted in
the battery for the generation of electricity while a first exhaust
gas is produced. The remainder of the combustion gas is burned in
the burner while producing a second exhaust gas, and the first
exhaust gas used at least partly as an oxygen source in the
process. Heat for heating purposes is gained from the exhaust
gases, with at least about half of the water contained in the
exhaust gases being condensed out.
A plant for carrying out the method includes a stack of fuel cells,
a burner, at least one heat exchanger and a consumer system.
It is advantageous for the named stack of fuel cells to comprise a
stack of planar cells which is arranged in a heat insulating
sleeve, with a channelling system by means of which the input air
is preheated being contained in the sleeve. A prereformer is placed
ahead of the stack, which is executed in a centrally symmetric
manner for example, in which the hydrocarbons, in particular
methane, are converted to carbon monoxide and hydrogen in the
presence of water and with the absorption of heat. The fuel cells
must be operated with a relatively large air surplus in order that
no detrimental temperature gradients arise. The stoichiometric
ratio must be greater than about 3; i.e. in the case that the
combustion gas contains methane, at least about 6 moles of oxygen
instead of 2 moles must be made available per mole of methane for
converting the methane into carbon monoxide and water.
Also, in order to have available as large an amount of heat for
heating purposes as possible, at least half of the copiously
arising water vapor is condensed out in accordance with the
invention during the heat extraction from the exhaust gases of the
burner and the battery in such a manner that the heat of
condensation is exploited. Since the exhaust gas of the battery
contains a considerable percentage of oxygen, this can be used
during the combustion in the burner. Here, it is important for the
invention that the water vapor contained in this exhaust gas also
appears as a constituent of the burner exhaust gas and thus
continues to be available for use in heating.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a stack of fuel cells,
FIG. 2 is a plant by means of which the method in accordance with
the invention can be carried out,
FIG. 3 shows illustrations of the reactions taking place in the
battery and in the gas burner,
FIG. 4 is a schematic diagram of the plant of FIG. 2,
FIGS. 5, 6 show schematic diagrams of each of two further plants in
accordance with the invention, and
FIG. 7 is a schematic diagram of a plant with a lambda probe.
DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS
The stack of fuel cells C in FIG. 1 is to be understood as an
example. A different example is described in the European patent
application No. 96810410.9 (P.6739). Further details are also
disclosed there which are not dealt with here.
The battery C comprises a stack 1 of substantially centrally
symmetrical high temperature fuel cells 10, a prereformer 3, a
sulphur absorber 4 and a sleeve 2. A first channelling system of
the sleeve 2 has the following parts: ring-gap-like chambers 21, 22
as well as 23, an air-impermeable body 25 of a heat insulating
material and an air-permeable body 26 which enables a radial air
inflow from the chamber 22 into the chamber 23. Air can be fed in
from the chamber 23 through an afterburner chamber 12 into the
cells 10 via tubelets 12'. A second channelling system 7 in the
lower part of the battery C represents a heat exchanger by means of
which heat can be supplied to the prereformer 3 and the sulphur
absorber 4. A ring-gap-like jacket chamber 5 about the sulphur
absorber 4 is executed as a vaporizer for water W.
The combustion gas G required for the current yielding reactions is
fed in centrally into the cell stack 1 via the absorber 4, the
prereformer R and a line 13.
During a start up phase, a hot combustion gas is fed through a tube
6 into the battery C in order to heat up the latter. After flowing
through the second channelling system 7 and the afterburner chamber
12, the combustion gas leaves the battery C through a tube 8. After
being heated up, the battery C can be brought into a
current-delivering operating state. During this operating state,
hot exhaust gas flows out of the afterburner chamber 12 in the
opposite direction through the second channelling system 7 to an
outlet 9, whereupon the exhaust gas yields up the heat required in
the prereformer 3 and the vaporizer 5. The flow of the hot
combustion gas or of the exhaust gas respectively is controlled by
the blocking members (flaps) 60, 80 and 90.
In the plant in accordance with the invention of FIG. 2 the battery
C is combined with a gas burner B in a special manner. During the
current-delivering operating state the exhaust gas of the battery C
is led via a line 91 into a first heat exchanger E1, for example a
heater for utility water 95, and subsequently--line 92--fed into
the burner B, where the oxygen contained in the exhaust gas is used
for the combustion of the gas G. (In a utility water heating it is
advantageous to use a storage, namely a boiler, in which fresh
water flows into the bottom of the boiler as heated water is
removed. The heating and the removal of the water are carried out
here in a known manner such that a lower cold zone coexists with an
upper warn zone.) The combustion gas of the burner B--line 62--is
conducted through a second heat exchanger E2 and the heat won there
is used for a room heating H. It is envisaged in accordance with
the invention that water vapor of the combustion gas is condensed
out in the heat exchanger E2. The cooled combustion gas 65 is
conveyed via a line 64 to a non-illustrated chimney.
For the heating up during the starting phase, the combustion gas,
which can be produced by the burner B, can be supplied via the line
61 to the battery C--with open blocking members 60 and 80 as well
as with closed blocking members 63 and 90. The cooled combustion
gas enters the line 62 leading to the heat exchanger E2 via the
line 81. If the burner B is used for heating the battery C, air
must be taken directly from the surroundings (not shown in FIG.
2).
In the upper half of FIG. 3 it is shown that the educts methane,
water and oxygen are converted in the battery C via the reactions
R, C1 and C2 into the products carbon dioxide and water, which
leave the battery with the exhaust gas. In the present example,
oxygen is fed in in the threefold amount with respect to the
stoichiometric requirement. The unused portion of the oxygen also
appears in FIG. 3 as part of the exhaust gas.
The reaction R, namely a reforming, converts methane into the
electrochemically utilizable intermediary products hydrogen and
carbon monoxide. A corresponding reforming is also possible if
other hydrocarbons are used. The reactions C1 and C2 are those
electrochemical reactions as a result of which the electrical
energy is generated. Together with the oxygen, further constituents
of the air (nitrogen) flow through the battery, which are not shown
in FIG. 3 for the sake of clarity.
The lower half of FIG. 3 shows a combustion taking place in the
burner B, namely the combustion of methane using the exhaust gas of
the battery C in accordance with the method of the plant shown in
FIG. 2. The combustion gas produced contains 7 parts of H.sub.2 O
for 3 parts of CO.sub.2, with 1 part of CO.sub.2 and 3 parts of
H.sub.2 O having already been supplied to the burner B in the
exhaust gas of the battery C. On the basis of FIG. 3 it becomes
evident that water vapor is an essential component of the exhaust
gases. The method in accordance with the invention is particularly
advantageous since the water vapor contained in the battery exhaust
gas appears as a constituent of the burner exhaust gas and is thus
also available for use in heating.
The schematic diagrams of FIGS. 4 to 6 show three examples for
plants in accordance with the invention in which a battery C, a
burner B and one or two heat exchangers E or E1 and E2 respectively
are combined. A first exhaust gas is formed in the battery C, a
second exhaust gas in the burner B.
The combination of FIG. 4 corresponds to the plant of FIG. 2. The
supply of the means air A, gas G and water W is symbolized in a
simplified manner by the arrow 100, with these means in reality
being fed into the battery B at different locations. The
connections 910 and 920 correspond to the lines 91 and 92
respectively in FIG. 2. The dashed arrow 930 indicates that the
first exhaust gas need not be conducted to the burner B in its
entirety. If the air surplus in the battery C is large, it is
advantageous if only a part of the first exhaust gas is used in the
burner B. The arrow 650 corresponds to the arrow 65 in FIG. 2 and
represents the flow of exhaust gas to a chimney. In the first heat
exchanger it is advantageous not to perform a condensation of the
water vapor. The condensation proceeds from the second exhaust gas
in the heat exchanger E2.
FIG. 5 shows substantially the same circuit as in FIG. 4. The
difference is that the first exhaust gas is conveyed via the
connection 900 directly into the burner B without a removal of heat
taking place in a first heat exchanger. The heat utilization in
accordance with the invention takes place in the single heat
exchanger E.
In the plant of FIG. 6 the exhaust gases of the battery and the
burner are conducted to the single heat exchanger E as a mixture. A
part of the cooled exhaust gas is conveyed back into the burner B
via the connection 950. The connection 600 in dashed lines
indicates that the combustion gas of the burner can be used for
heating up the battery (start up phase).
FIG. 7 shows a schematic diagram of a plant with a lambda probe D1
which is placed after the burner and by means of which the oxygen
content of the exhaust gas can be measured. This probe is a
component of a control system which regulates by means of a logic
circuit D the supply of the combustion gas (control member D2)
and/or of the exhaust gas of the fuel cells (control member D3)
into the burner. If natural gas is used, it is advantageous for the
control system to ensure that at least 2.2 moles of molecular
oxygen per mole of methane are fed into the burner B.
The first exhaust gas, i.e. the exhaust gas that arises in the
battery of fuel cells, has a relatively low dew point (condensation
temperature of the water vapor). At a stoichiometric ratio of 5 for
the air surplus and at an efficiency of 50% for the electrical
energy, the dew point lies at 42.degree. C. Corresponding pairs of
figures for the air surplus/dew point are: 3.63/48.3.degree. C. and
10/31.0.degree. C. For a return flow temperature of a heating
system, which typically amounts to 30.degree. C., only little heat
can be won by water condensation in a heat exchanger which is
placed after the stack of fuel cells.
Thanks to the method in accordance with the invention, the water
vapor contained in the first exhaust gas appears in the second
exhaust gas--the exhaust gas of the burner--at a higher dew point.
The elevation of the dew point amounts to several degrees Celsius
and it holds that: the greater the air surplus in the battery, the
greater this elevation is. In accordance with the higher dew point,
more heat is obtained through condensation with the return flow of
the named heating system.
Compared with a method in which air is taken directly from the
surroundings as an oxygen source for the burner, there results an
improvement of the total efficiency (=ratio of heat energy plus
electrical energy won to the energy content of the combustion gas)
of several percent. At an air surplus of 7 for the battery and 1.5
for the burner, at a utilisation of 20% of the combustion gas in
the battery and 80% in the burner, at an electrical efficiency of
50%, further at a heating of the return flow from 30 to 40.degree.
C. in the heat exchangers E2 (first) and E1 in accordance with the
exemplary embodiment of FIG. 4, there results an increase in the
total efficiency of about 6%. The dew point of the second exhaust
gas amounts to 55.8.degree. C. in this example, whereas it amounts
to only 35.1.degree. C. for the first exhaust gas. The heat won
through condensation amounts to about 8% of the total usable
energy.
* * * * *